1. Field of the Invention
The invention relates generally to the field of directional drilling of wellbores through subsurface rock formations. More particularly, the invention relates to techniques for determining the geodetic trajectory and position of a directionally drilled wellbore using seismic techniques.
2. Background Art
Wellbores drilled through subsurface rock formations are used for, among other purposes, extracting oil and gas from subsurface reservoirs. Many wellbores are drilled to have a selected trajectory, that is to say, along a selected geodetic path through the subsurface other than substantially vertical, using various techniques known collectively as “directional drilling.” Directional drilling enables having a single wellbore penetrate one or more subsurface reservoirs that are located at substantial geodetic distances from the surface location of the wellbore. Although not limited to such use, a common use for directional drilling is to enable penetrating a number of laterally separated subsurface reservoirs from a single marine platform. Directional drilling is also used in environmentally sensitive areas, such as the Arctic, where it is desirable to minimize the area at the surface affected by drilling operations.
An important aspect of directional drilling is accurate surveying of the wellbore trajectory so that the spatial position of the wellbore in three dimensions is known precisely at every point along the wellbore. Typical techniques for surveying include gyroscopic surveying and combination magnetic/gravitational surveying. See, for example, U.S. Pat. No. 4,920,655 issued to van Steenwyk for an example of gyroscopic survey instrumentation. U.S. Pat. No. 7,405,563 issued to Kruspe et al. describes an example magnetic/gravitational survey instrument. Using the foregoing surveying techniques, however, can result in wellbore position determination that becomes less accurate with increasing lateral distance from the surface position of the wellbore. Less certainty in positioning the wellbore can result, for example, in increased risk of collision of a wellbore with an adjacent wellbore in cases where a plurality of wellbores are drilled from a single surface location or similar cases where wellbores are proximate each other. Loss of positional accuracy may result in one or more target reservoirs not being penetrated by the wellbore, which may require expensive and time consuming replacement of the wellbore to penetrate such targets.
Accordingly, there continues to be a need to wellbore trajectory determination methods that have improved accuracy.